Various pyrazolone derivatives have been known as magenta color image-forming couplers (referred to hereinafter simply as "magenta couplers"). However, these pyrazolone derivatives generally have low color formation efficiency (ratio of conversion of the coupler into a dye) when contained in photographic light-sensitive materials, and so-called 4-equivalent couplers, in which coupling position is not substituted, usually from only about 1/2 mol of dye per mol of the coupler.
To improve color formation efficiency, so-called 2-equivalent magenta couplers have been used, in which a substituent is introduced into the coupling position of a pyrazolone type magenta coupler, and the substituent splits off in the color development step. Examples of such couplers are disclosed, for example, in U.S. Pat. Nos. 3,331,476, 3,419,391, 3,617,291, and 3,926,631. Further, magenta couplers in which a substituent is linked to the coupling position through a sulfur ion are described in U.S. Pat. No. 3,214,437 (a thiocyano group), U.S. Pat. No. 4,032,346 (an acylthio group or a thioacylthio group), U.S. Pat. Nos. 3,227,554 and 3,701,783 and Japanese Patent Publication No. 34044/78 (an arylthio group or a heterocyclic thio group), and West German Patent Application (OLS) No. 2,944,601 (an alkylthio group).
It has been found as the result of the detailed investigations that when couplers having an arylthio group at the coupling active position among the magenta couplers described in U.S. Pat. Nos. 3,227,554 and 3,701,783 are used in a color photographic light-sensitive material and color images are formed, the light fastness of the color images does not completely satisfy the desired improvement in the properties of the color photographic light-sensitive materials.
Also, it has been found that when the magenta couplers which release an arylthio group as described in Japanese Patent Publication No. 34044/78 are used in a color photographic light-sensitive material and color images are formed, the light fastness of the color images is insufficient.